1. Field of the Invention
The invention relates to an electrical air heating apparatus, in particular for a motor vehicle, with electrical heating elements for heating the air and a housing which has a ground connection, an electrical supply connection and an electronic circuit to control the supply of the heating elements and at which the heating elements are arranged in electrical contact with the ground connection and the electrical supply connection.
2. Description of Related Art
Such an electrical air-heating apparatus in which the electrical heating elements are formed of PTC heating rods is known. In the known heating apparatus, the housing is made of a plastic material in which the heating elements are provided in a casting or sealing compound and are connected to the electrical supply connection via the electronic circuit on one side and to the ground connection via a ground plate and a ground pin electrically connected thereto on the other side.
In the known heating apparatus, the thermal and the mechanical connection between the housing, the electronic circuit and the heating elements is achieved by means of a plurality of components, wherein it is necessary to provide additional fillers, such as adhesives and sealing compounds, to achieve high compensation for tolerances. As well as the actual sealing function, the adhesives and sealing compounds also take on the function of absorbing any forces and moments of the heating apparatus. In this case, however, the sealing and connection between the plastic housing and the heating elements, which are generally formed of aluminum heating rods, are not easily processed and are unreliable. The required lifetime cannot be ensured so far. Furthermore, in the known heating apparatus, the forces appearing are transmitted up to the printed circuit board on which the electronic circuit is provided. As a result of this transmission, there may be some mechanical stressing of the printed circuit board which is associated with a high risk of damage to the electronic components.
Thus, a primary object of the present invention is to provide an electrical air heating apparatus of the type specified initially which manages with a smaller number of components, especially in the region of its housing.
This object is achieved according to the invention by the housing being constructed of an electrically conducting material in one piece with a molded-on ground connection, and the heating elements and the electronic circuit are arranged in direct electrical contact with the housing.
As a result of the fact that, in the heating apparatus according to the invention, the housing is made of an electrically conducting material and is constructed in one piece with the ground connection, the ground potential lies at the housing so that this not only fulfils the housing function, but also the function of the ground plate, the ground pin and the ground connection for adaptation by the customer, which are present in the known heating apparatus. This has the consequence that the ground plate, the ground pin and the sealing compound which are provided as separate components in the known heating apparatus, are dispensed with in the heating apparatus according to the invention.
Further developments and embodiments of the heating apparatus according to the invention have the advantage that heat can be conducted and removed from the printed circuit board carrying the electronic circuit and the power switches into the heating region, that heat exchange can take place without surface loss by heat transport via breaks in the housing with weight optimization, and that the mechanical fixing of all the components, the fixing of the printed-circuit board, the entire ground contacting of the heating apparatus and the direct ground contacting can be made polarity-safe via the ground connection molded on to the housing for a customer""s cable.
In terms of production, there are the advantages that, as a result of the smaller number of components, the number of production steps in series production is smaller and that automated methods can be used.
In addition, the mechanical heat-transfer interfaces for the removal of thermal energy from the power switches into the heating regions are simpler and the heat from the power switches is removed directly via the housing into the actual heating region, wherein the ground contacting can be made polarity-safe via the ground connection and the forces and moments from the heating region can be absorbed without providing additional components.
Preferred embodiments of the heating apparatus according to the invention are described in detail in the following with reference to the accompanying drawings.